Allow mesh material homogenization to include or exclude voids (openm…

…c-dev#3000)

openmc/mesh.py

@@ -152,6 +152,7 @@ def get_homogenized_materials(
             model: openmc.Model,
             n_samples: int = 10_000,
             prn_seed: Optional[int] = None,
+            include_void: bool = True,
             **kwargs
     ) -> List[openmc.Material]:
         """Generate homogenized materials over each element in a mesh.
@@ -168,6 +169,8 @@ def get_homogenized_materials(
         prn_seed : int, optional
             Pseudorandom number generator (PRNG) seed; if None, one will be
             generated randomly.
+        include_void : bool, optional
+            Whether homogenization should include voids.
         **kwargs
             Keyword-arguments passed to :func:`openmc.lib.init`.
 
@@ -222,6 +225,10 @@ def get_homogenized_materials(
                 material_ids.pop(index_void)
                 volumes.pop(index_void)
 
+            # If void should be excluded, adjust total volume
+            if not include_void:
+                total_volume = sum(volumes)
+
             # Compute volume fractions
             volume_fracs = np.array(volumes) / total_volume
 

tests/unit_tests/test_mesh.py

@@ -386,3 +386,9 @@ def test_mesh_get_homogenized_materials():
 
     # Mesh element that overlaps void should have half density
     assert m4.get_mass_density('H1') == pytest.approx(0.5, rel=1e-2)
+
+    # If not including void, density of homogenized material should be same as
+    # original material
+    m5, = mesh_void.get_homogenized_materials(
+        model, n_samples=1000, include_void=False)
+    assert m5.get_mass_density('H1') == pytest.approx(1.0)